What if there is a power outage? You say battery? What if the battery fails? And you would still have the problem of keeping thousands of batteries and electronics running, those fail too. In the end you are adding complexity to the system, so physical locks still have advantages.
Anyway, it's not a trivial modification, ie. just replacing the lock, because the digital lock needs power to process the key and unlock the door. As long as that's necessary, the initial investment and the increased complexity make the benefits moot to me personally. If you have some sort of door knob action maybe you could harness that to generate a small amount of power sufficient to unlock the door?